EP2001126A1 - Bidirectional frequency mixer, radiofrequency emitter/receiver system comprising at least one such mixer - Google Patents

Abstract

The mixer (9) has phase difference units distributing signal on mixing cells, and another set of phase difference units distributing power of signal on each cells. Third set of phase difference units distribute power of signal on each mixing cell, and one of the sets of phase difference units combine the signals provided from the cells to produce radio signal free of a phase opposition frequency component, where the combined signals comprises the phase opposition frequency components and phase frequency components. An independent claim is also included for a method for implementing a device for mixing signals.

Description

The present invention relates to a bidirectional frequency mixer, as well as a radiofrequency transmitter / receiver system comprising at least one such mixer. It is particularly applicable in the design of microwave integrated circuits, particularly in the millimetric frequency band.

Radio frequency communication systems generally include receiving and transmitting devices such as antennas, a processing unit and an interface for the exchange of signals between the transmitting / receiving devices and the processing unit.

In order, on the one hand, to render usable by a processing unit a signal received by the transmission / reception device, and on the other hand to be able to transmit a signal produced by the processing unit, the reception and reception functions The transmission generally comprises amplification, filtering, mixing and modulation / demodulation steps. Mixers are, among other things, used to transpose high frequency signals to lower frequency bands to facilitate processing. In particular, the use of certain filters, computers or demodulators sometimes require working at lower frequencies, called intermediate frequencies.

One of the problems with communications systems is simultaneous transmission / reception, or at least transmission / reception in half-duplex mode. In particular, an additional difficulty arises with the use of the mixers. In fact, unwanted frequency signals generated during a mixture, whether in the reception phase or in the transmission phase, appear.

In order to respond to these problems, it is known to use a signal-emitting chain separate from the receiver chain, as shown in FIG. figure 1 . Each of these two processing chains then has its own components and can operate without significantly disturbing the concomitant chain. Such a structure has the particular disadvantage of increasing the cost and size of the circuit. In particular, at least two mixers 6, 7 are required, one for the reception phase which converts the high frequency signals to an intermediate frequency and the other for the transmission phase which converts the signals from the processing unit to a higher frequency. In millimetric frequency band, these elements can in particular be integrated on a microwave integrated circuit still called MMIC according to the Anglo-Saxon expression "Monolithic Microwave Integrated Circuit". However, the number and size of the components to be integrated on this type of circuit is an important criterion to be taken into account in the design phase.

The figure 1 presents a radiofrequency transmitter / receiver system according to the prior art. The system 1 comprises an antenna 2, a switching device 3, a processing unit 4, a local oscillator 5 and two mixers 6 and 7.

In the reception phase, an _{RF RF} signal S _RF captured by the antenna 2 is transmitted by the switching device 3 to a first input 6a of the first mixer 6. By combining the signal S _RF with a frequency signal F _OL supplied on a second input 6b by the local oscillator 5, the first mixer 6 produces a signal S _FI on an output 6c at an intermediate frequency FI compatible with the operation of the processing unit 4.

In the transmission phase, the processing unit 4 supplies on a first input 7c of the second mixer 7 a signal S _FI 'of frequency FI. By combining the signal S _FI 'with a signal of frequency F _OL supplied by the local oscillator 5 on a second input 7b, the second mixer 7 produces on an output 7a an _RF signal S _RF '. The _RF signal S 'is then transmitted by switching 3 to the antenna 2 which can transmit it.

• o un mode réception, combinant un signal radioélectrique S_RF+IM comprenant une composante fréquentielle RF et une composante fréquentielle image IM avec un signal S_FOL de fréquence F_OL pour produire un signal S_FI de fréquence intermédiaire FI,
• o un mode émission, combinant un signal S_FI de fréquence intermédiaire FI avec un signal S_FOL de fréquence F_OL pour produire un signal radioélectrique S_RF,

le mélangeur comportant au moins :

• o quatre cellules de mélange, chacune étant adaptée à combiner deux signaux pour produire un signal de sortie transposé en fréquences par rapport au premier des deux signaux,
• o un premier moyen de déphasage adapté à répartir le signal S_FOL sur chaque cellule de mélange,
• o un deuxième moyen de déphasage adapté, en réception, à répartir la puissance du signal S_RF+IM sur chaque cellule de mélange,
• o un troisième moyen de déphasage adapté, en réception, à combiner les signaux issus desdites cellules de mélange pour produire un signal S_FI exempt de la composante fréquentielle IM, les signaux combinés comprenant des composantes fréquentielles image IM en opposition de phase et des composantes fréquentielles FI en phase,

le troisième moyen de déphasage étant également adapté, en émission, à répartir la puissance du signal S_FI sur chaque cellule de mélange, et, le deuxième moyen de déphasage étant également adapté, en émission, à combiner les signaux issus desdites cellules de mélange pour produire un signal radioélectrique S_RF exempt de la composante fréquentielle F_OL, les signaux combinés comprenant des composantes fréquentielles F_OL en opposition de phase et des composantes fréquentielles RF en phase.An object of the invention is in particular to use a single mixer common to the transmission and reception chains performing a rejection of unwanted frequencies in the reception phase and in the transmission phase. For this purpose, the subject of the invention is a bidirectional signal mixer adapted to operate in two modes:

• a reception mode, combining a radio signal S _{RF + IM} comprising a frequency component RF and an image frequency component IM with a signal S _FOL of frequency F _OL to produce an _IF signal of IF intermediate frequency,
• o a transmission mode, combining an intermediate frequency IF signal S _IF with a frequency signal S _FOL F _OL to produce a radioelectric signal S _RF,

the mixer comprising at least:

• four mixing cells, each being adapted to combine two signals to produce an output signal transposed in frequencies with respect to the first of the two signals,
• a first phase shift means adapted to distribute the signal S _FOL on each mixing cell,
• a second means of phase shift adapted, in reception, to distribute the power of the signal S _{RF + IM} on each mixing cell,
• a third phase shift means adapted, in reception, to combine the signals from said mixing cells to produce a signal S _FI free of the frequency component IM, the combined signals comprising counter-phase IM image frequency components and frequency components FI in phase,

the third phase-shifting means being also adapted, in transmission, to distribute the power of the signal S _FI on each mixing cell, and, the second phase-shifting means being also adapted, in transmission, to combine the signals coming from said mixing cells to producing a radio signal S _RF free of the frequency component F _OL , the combined signals comprising frequency components F _OL in opposite phase and RF frequency components in phase.

According to one embodiment, the first phase-shifting means comprises at least one coupler adapted to distribute the power of an input signal on two output signals, the first output signal S _FOL ^{90 °} being out of phase with respect to the second signal output S _FOL ^{0 °} .

The first phase-shifting means may comprise a power divider and two couplers, said divider distributing the power of the signal S _FOL on an input of each coupler, each coupler distributing the power of its incoming signal on two output signals, the first signal of output S _FOL ^{90 °} being out of phase with the second signal S _FOL ^{0 °} output.

• o à répartir, en sortie des deuxième et troisième coupleur, la puissance du signal S_RF+IM reçu par une entrée-sortie du premier coupleur,
• o et/ou à combiner les signaux reçus par les deuxième et troisième coupleur pour produire un signal S_RF sur une entrée-sortie du premier coupleur.

The second phase-shifting means may comprise at least three couplers, a first input-output of the first coupler being connected to a input-output of the second coupler, and a second input-output of the first coupler being connected to an input-output of the third coupler, the second and third coupler being connected to the mixing cells, so as:

• o distributing, at the output of the second and third couplers, the power of the signal S _{RF + IM} received by an input-output of the first coupler,
• and / or combining the signals received by the second and third couplers to produce an _RF signal S on an input-output of the first coupler.

• o à répartir, en sortie des deuxième et troisième coupleur, la puissance du signal S_FI reçu par une entrée-sortie du premier coupleur,
• o et/ou à combiner des signaux reçus par les deuxième et troisième coupleur pour produire un signal S_FI sur une entrée-sortie du premier coupleur.

The third phase-shifting means may comprise at least three couplers, a first input-output of the first coupler being connected to an input-output of the second coupler, and a second input-output of the first coupler being connected to an input-output of the third coupler. , the second and third couplers being connected to the mixing cells, so as to:

• o distributing, at the output of the second and third couplers, the power of the signal S _FI received by an input-output of the first coupler,
• and / or combining signals received by the second and third couplers to produce an _IF signal on an input-output of the first coupler.

• o sur une durée Δt1, on combine un signal d'entrée de fréquence RF avec un signal d'entrée de fréquence Fol afin de produire en sortie un signal de fréquence FI,
• o sur une durée Δt2, décalée dans le temps par rapport à Δt1, on combine un signal d'entrée de fréquence FI avec un signal d'entrée de fréquence Fol afin de produire en sortie un signal de fréquence RF.

The invention also relates to a method for implementing a bidirectional signal mixer as described above, comprising the following steps:

• o over a duration Δt1, an RF frequency input signal is combined with a frequency input signal Fol in order to output an IF frequency signal,
• o over a time Δt2, shifted in time with respect to Δt1, an IF frequency input signal is combined with a frequency input signal Fol in order to output an RF frequency signal.

The invention also relates to a radiofrequency transmitter / receiver system comprising at least one bidirectional mixer comprising the characteristics described above.

• la figure 1, un système émetteur/récepteur radiofréquences selon l'art antérieur, la figure a déjà été présentée,
• la figure 2, un système émetteur/récepteur radiofréquences comportant un mélangeur bidirectionnel de fréquences selon l'invention,
• la figure 3, un exemple de réalisation d'un mélangeur selon l'invention avec des indications fléchées sur les sens de propagation des signaux correspondant à la phase de réception,
• la figure 4, un exemple de réalisation d'un mélangeur selon l'invention avec des indications fléchées sur les sens de propagation des signaux correspondant à la phase d'émission,
• la figure 5 un exemple d'utilisation du mélangeur selon l'invention.

Other features and advantages will become apparent on reading the following illustrative and nonlimiting detailed description given with regard to appended drawings which represent:

• the figure 1 , a radiofrequency transmitter / receiver system according to the prior art, the figure has already been presented,
• the figure 2 a radiofrequency transmitter / receiver system comprising a bidirectional frequency mixer according to the invention,
• the figure 3 an embodiment of a mixer according to the invention with indications on the direction of signal propagation corresponding to the reception phase,
• the figure 4 an embodiment of a mixer according to the invention with indications on the direction of signal propagation corresponding to the transmission phase,
• the figure 5 an example of use of the mixer according to the invention.

The figure 2 presents a transmitter / receiver system of a bidirectional mixer 9, according to the invention, allowing the conversion of the signals in the reception phase and in the transmission phase.

A system 8, whose detailed operation is described below, operates in a half-duplex mode. The system 8 comprises the bidirectional mixer 9, a signal processing device 10, an antenna 11 and a local oscillator 12 providing a transposition frequency. The mixer 9 comprises a first input 9b, a second input 9d, an input-output 9a and an output 9c. The system 8 operates for example as described below.

During a period of time Δt1, the system 8 operates in reception mode, that is to say that the antenna 11 captures external signals. These signals are transmitted to the mixer 9, then to the processing unit 10. When the period Δt1 is complete, the antenna 11 switches to emission for a duration Δt2, for example. The mixer 9 does not necessarily have a switching device to switch from one mode to another. The presence or absence of signals on the input-output 9a is sufficient, in the example, to define the mode of operation. The signals from the processing unit 10, are then transmitted to the mixer 9 and to the antenna 11 which emits. When the period Δt2 is complete, the antenna 11 switches back to receive mode for a duration Δt1 and the cycle starts again.

The mixer 9 is described as bidirectional in the sense that it can perform a frequency transposition in both directions, that is to say convert signals from a frequency A to a frequency B and from frequency B to frequency A.

In the reception phase, the bidirectional mixer 9 receives on the input-output 9a a signal _RF of _RF frequency coming from the device of the antenna 11, and on the first input 9b a signal S _Fol of frequency Fol produced by the local oscillator 12. The role of the mixer 9 is then to convert the signal S _RF to a signal S _FI delivered by the output 9c, of reduced intermediate frequency IF equal to | RF-Fol |. For example, a mixer can be used in a radiofrequency transmitter / receiver, which receives a carrier wave at an RF frequency equal to 40 Ghz and must transpose this signal at an intermediate frequency FI equal to 5 Ghz. In this case, the local oscillator delivers an RF-FI frequency signal equal to 35 Ghz or RF + FI frequency equal to 45 Ghz. In the exemplary embodiment developed in this description, the transposition frequency Fol is chosen to be less than RF and therefore Fol = RF-Fl.

However, the input signal S _RF can be noisy. It may in particular contain a parasitic frequency component at the IM frequency equal to Fol-FI, this is what the skilled person commonly calls the image frequency. Since the mixer 9 acts over a wide band of the frequency spectrum, this noise S _IM at the frequency IM can be transposed to the frequency | IM-Fol | equal to FI and disturb the signal from the output 9c by adding to the wanted signal. A mixer 9 according to the invention performs a rejection of the image frequency IM and the signal from the output 9c is then composed of two main frequency components: FI and Fol. The frequency Fol undesirable can be easily filtered because it is generally much higher than FI.

In the transmission phase, the mixer 9 receives on the second input 9d a signal S _FIT of frequency F1 and on the first input 9b a signal S _FOL of frequency Fol which can be produced by the same local oscillator 12 as for the phase of reception. The role of the mixer 9 is then to convert the signal S _FIT to a higher frequency signal RF outgoing on the input-output 9a. It is then the antenna 11 which emits this signal.

The mixer 9 uses a signal S _Fol generally high power to perform a frequency transposition for the emission. As will be described later, a mixer may output a portion of the power at the input frequencies. However, it is necessary to avoid transmitting the Fol component through the input-output 9a, because Fol being relatively close to RF, and all the closer to RF that FI will be small, it would then be difficult to eliminate this frequency Fol by filtering. According to a method described later in relation to the figure 3 the mixer 9 thus operates a rejection of the frequency Fol and the signal from the input-output 9a is then composed of the only RF frequency component.

According to another mode of operation, the system 8 comprises two antennas, a first for the transmission and a second for the reception of the signals. In this case, the link 13 can be split, for example by means of a power divider, an input of the power divider being connected to the first antenna and another input being connected to the second antenna. This embodiment is not shown in the figures.

Filtering means or amplifiers, not shown here, can also be placed on the channels connecting the mixer 9 to the other elements 10, 11 and 12 of the system 8.

The figure 3 presents an exemplary embodiment of the invention with arrow indications representing the directions of propagation of the signals corresponding to the reception phase.

The bidirectional mixer 9 can be made by the use of passive elements such as a first coupler 14, a second coupler 15, a third coupler 16, a fourth coupler 17, a fifth coupler 18, a sixth coupler 25, a seventh coupler 26 and an eighth coupler 27 but also thanks to active elements such as a first mixing cell 19, a second mixing cell 20, a third mixing cell 21 and a fourth mixing cell 22.

The fifth coupler 18 includes a first input-output 18a, a second input-output 18b, a third input-output 18c, and a fourth input-output 18d. The signal entering through the first input-output 18a is power-distributed on the inputs-outputs 18b and 18c. On the third input-output 18c, the signal goes out of phase by 90 °, while it is transmitted in direct line and therefore without phase shift to the second input-output 18b. The fourth input-output 18d is simply connected to a resistive load 23. The other couplers 14, 15, 16, 17, 25 and 26, with the exception of the eighth coupler 27, function in a similar manner by effecting a phase shift of 90 °. The eighth coupler 27 comprises four input-outputs, a first input-output 27a, a second input-output 27b, a third input-output 9c and a fourth input-output 9d. When two signals enter respectively the first input-output 27a and the second input-output 27b, their powers are combined to exit on the third input-output 9c. When a signal is received by the fourth input-output 9c, it is distributed in power on the first and second input-outputs 27a, 27b. The signal then coming from the first input-output 27a is phase shifted by 180 ° while the signal coming from the second input-output 27b is not out of phase.

A first mixing cell 19 comprises a first access 19a, a second access 19b, and a third access 19c. It has the particular function of combining two input signals of respective frequencies A and B to produce an output signal having the following frequency components A, B, A + B and | AB |. These are the frequency components A + B and | AB | which are useful because they are those that make it possible to transpose an input frequency to another lower frequency, for example for reception, or higher, for example for transmission. The unwanted components may, for example, be filtered out. In the context of the operation described here, the first port 19a remains an input while the other two ports 19b and 19c operate in opposition and alternately become an input or an output of the cell 19 according to whether the mixer 9 is in reception or transmission mode . The Other mixing cells 20, 21, and 22 presented below operate in a similar manner.

In the reception phase, the input signal S _RF passes into the fifth coupler 18 which generates a signal S _RF ^{90 °} of the same frequency phase-shifted by 90 ° on its third input-output 18c, while its second input-output 18b produces a signal S _RF ^{0 °} of the same frequency and the same phase as S _RF . Moreover, the input signal S _RF may contain noise around the image frequency IM = Fol-FI. A noise S _IM on this frequency is potentially troublesome because it is transposed by a mixing cell at the intermediate frequency FI, thus parasitizing the useful signal. A noisy signal S _RF + S _IM is therefore transmitted in the first coupler 18 and the signals S _RF ^{0 °} + S _IM ^{0 °} and S _RF ^{90 °} + S _IM ^{90 °} leave this coupler respectively by its second 18b and its third input-output 18c. According to the same principle, the signals S _RF ^{0 °} + S _IM ^{0 °} and S _RF ^{90 °} + S _IM ^{90 °} pass respectively into the third and fourth couplers 16 and 17 via the first inputs-outputs 16a and 17a to undergo a phase shift 90 °. Thus, the second and third input-outputs 16c, 16b, 17b and 17c of the third and fourth couplers 16 and 17 all produce a signal at the noisy RF frequency, but each with their own phase shift. The signals S _RF ^{90 °} + S _IM ^{90 °} coming from the third input-output 16c of the third coupler 16 and the second input-output 17b of the fourth coupler 17 are phase shifted by 90 °, the signal S _RF ^{0 °} + S _IM ^{0 °} from the second input-output 16b of the third coupler 16 is not out of phase and the signal S _RF ^{180 °} + S _IM ^{180 °} from the third input-output 17c of the fourth coupler 17 is phase shifted by 180 °.

Similarly, the signal S _FOL produced by the local oscillator 12 is transmitted to the first and second couplers 14 and 15 after passing through a power divider 24 to distribute the signal to their two first inputs-outputs 14a and 15a. Following the same principle as for the third and fourth couplers 16 and 17, the signals leaving the first and second couplers 14 and 15 are of the same frequency Fol but of different phases. The signals S _FOL 90 ° from the third input-outputs 14c and 15c of the first and second couplers 14 and 15 are phase shifted by 90 ° while the signals S _FOL ^{0 °} from the second inputs-outputs 14b and 15b of the first and second couplers 14 and 15 are not out of phase.

According to another embodiment, the signals S _FOL ^{0 °} and S _FOL ^{90 °} produced at the output of the first and second couplers 14 and 15 are produced using a single coupler receiving the signal S _FOL produced by the local oscillator 12. power divider is then placed at each of the two outputs of said coupler to distribute the power of the two signals S _FOL ^{0 °} and S _FOL ^{90 °} into four signals of substantially equal powers. These four signals are then distributed at the output so as to present successively the same phase shifts as those produced by the previous embodiment, involving two couplers.

• o S_FOL ^90° avec S_RF ^90°+S_IM ^90° sur la première cellule de mélange 19,
• o S_FOL ^0° avec S_RF ^0°+S_IM ^0° sur la deuxième cellule de mélange 20,
• o S_FOL ^0° avec S_RF ^90°+S_IM ^90° sur la troisième cellule de mélange 21,
• o S_FOL ^90° avec S_RF ^180°+S_IM ^180° sur la quatrième cellule de mélange 22.

Selon le fonctionnement d'une cellule de mélange décrit plus haut, les composantes fréquentielles en sortie des cellules de mélange sont Fol, RF, IM, RF+Fol, IM+Fol, et FI=RF-Fol=Fol-IM. Les composantes Fol, RF, IM, et RF+Fol sont indésirables mais peuvent être filtrées aisément ultérieurement du fait de l'écart de valeur important entre ces fréquences et FI. Afin de rendre le propos plus clair, ces composantes, bien que potentiellement présentes dans le spectre de fréquence, seront donc ignorées dans la suite de la description. La composante fréquentielle FI est issue à la fois de RF-Fol et de Fol-IM, donc le spectre de fréquence en sortie est parasité par un signal créé par la transposition de la fréquence IM. Il faut donc supprimer ce signal parasite.
Un signal S_FI ^90° de fréquence FI issu du deuxième accès 21 b de la troisième cellule de mélange 21 est le produit de la transposition du signal S_RF ^90° déphasé de 90° et de fréquence RF par le signal S_FOL ^0° de fréquence Fol. Le bruit S_IM ^90° de fréquence image IM est également transposé en signal S_FI/IM ^-90° de fréquence FI. Mais ce signal S_FI/IM ^-90° est en opposition de phase par rapport au signal S_FI ^90° issu de la composante RF. Pour rappel, IM=Fol-FI et donc IM-Fol=-FI tandis que RF-Fol=Fl. En sortie du deuxième accès 21 b de la troisième cellule de mélange 21, il existe donc un signal de fréquence FI S_FI ^90°+S_FI/IM ^-90°. De manière similaire, la quatrième cellule 22 traite des signaux d'entrée S_FOL ^90° et S_RF ^180°+S_IM ^180° déphasés entre eux de 90°, donc le signal issu du deuxième accès 22b de la quatrième cellule de mélange 22 est le même que celui issu de 21 b. Pour les première et deuxième cellules 19 et 20, les signaux d'entrée S_FOL ^90° et SRF^90°+S_IM ^90° d'une part, et S_FOL ^0° et S_RF ^0°+S_IM ^0° d'autre part ne sont pas déphasés entre eux. Aux sorties des deuxièmes accès 19b et 20b des première et deuxième cellules de mélange, on retrouve donc des signaux non déphasés S_FI ^0°+S_FI/IM ^0°.The signals entering the first and third ports (19a and 19c), (20a and 20c), (21a and 21c), (22a and 22c) of each mixing cell 19, 20, 21 and 22 produce the following combinations :

• o S _FOL ^{90 °} with S _RF ^{90 °} + S _IM ^{90 °} on the first mixing cell 19,
• o S _FOL ^{0 °} with S _RF ^{0 °} + S _IM ^{0 °} on the second mixing cell 20,
• o S _FOL ^{0 °} with S _RF ^{90 °} + S _IM ^{90 °} on the third mixing cell 21,
• o S _FOL ^{90 °} with S _RF ^{180 °} + S _IM ^{180 °} on the fourth mixing cell 22.

According to the operation of a mixing cell described above, the frequency components at the output of the mixing cells are Fol, RF, IM, RF + Fol, IM + Fol, and FI = RF-Fol = Fol-IM. The components Fol, RF, IM, and RF + Fol are undesirable but can be filtered easily later because of the large difference in value between these frequencies and FI. In order to make the point clearer, these components, although potentially present in the frequency spectrum, will therefore be ignored in the remainder of the description. The frequency component F1 comes from both RF-Fol and Fol-IM, so the output frequency spectrum is parasitized by a signal created by the transposition of the frequency IM. It is therefore necessary to suppress this parasitic signal.
A signal S _FI ^{90 °} of frequency IF coming from the second port 21b of the third mixing cell 21 is the product of the transposition of the signal S _RF ^{90 °} phase-shifted by 90 ° and RF frequency by the signal S _FOL ^{0 °} of Fol frequency. The noise S _IM ^{90 °} of IM image frequency is also transposed into signal S _{FI / IM} ^{-90 °} of frequency FI. But this signal S _{FI / IM} ^{-90 °} is in phase opposition with respect to the signal S _FI ^{90 °} from the RF component. As a reminder, IM = Fol-FI and therefore IM-Fol = -FI while RF-Fol = Fl. At the output of the second port 21b of the third mixing cell 21, there is therefore a frequency signal FI S _FI ^{90 °} + S _{FI / IM} ^{-90 °} . Similarly, the fourth cell 22 processes the input signals S _FOL ^{90 °} and S _RF ^{180 °} + _SMI ^{180 °} phase-shifted by 90 °, therefore the signal from the second port 22b of the fourth mixing cell 22 is the same as the one from 21 b. For the first and second cells 19 and 20, the input signals S _FOL ^{90 °} and SRF ^{90 °} + S _IM ^{90 °} on the one hand, and S _FOL ^{0 °} and S _RF ^{0 °} + S _IM ^{0 °} d ' on the other hand are not out of phase with each other. At the outputs of the second ports 19b and 20b of the first and second mixing cells, therefore, there are non-phase-shifted signals S _FI ^{0 °} + S _{FI / IM} ^{0 °} .

The signals from the second ports 19b and 22b of the first and fourth mixing cells 19 and 22 are recombined in the sixth coupler 25 and the signals from the second ports 20b and 21b of the second and third mixing cells 20 and 21 are recombined in FIGS. the seventh coupler 26.

• o pour le sixième coupleur 25, S_FI ^0°+90°+S_FI/IM ^0°+90° (troisième entrée-sortie 25c déphasée) avec S_FI ^90°+S_FI/IM ^-90° (deuxième entrée-sortie 25b non déphasée),
• o pour le septième coupleur 26, S_FI ^0°+90°+S_FI/IM ^0°+90° (troisième entrée-sortie 26c déphasée) avec S_FI ^90°+S_FI/IM ^-90° (deuxième entrée-sortie 26b non déphasée).

Les puissances entre les entrées étant sensiblement également réparties, c'est donc le signal S_FI ^0°+90°+S_FI/IM ^0°+90°+S_FI ^90°+SFI/IM^-90°=S_FI ^90° qui sort de la première entrée-sortie 25a du sixième coupleur avec une puissance en sortie double que le signal S_FI ^90° entré par la deuxième entrée-sortie 25b du sixième coupleur, ceci grâce à la combinaison des deux signaux entrés par les deuxième et troisième entrées-sorties 25b et 25c. Le septième coupleur 26 appliquant la même opération que le sixième coupleur 25 sur des signaux d'entrée identiques, c'est également un signal S_FI ^90° qui sort de la première entrée-sortie 26a du sixième coupleur. Les signaux S_FI/IM ont été éliminés grâce à la recombinaison des signaux sensiblement de même puissance S_FI/IM ^90° et S_FI/IM ^-90° en opposition de phase. Le mélangeur 9 opère donc une réjection de la fréquence image lors de la phase de réception.Thus, the sixth coupler 25 receives the signal S _FI ^{0 °} + S _{FI / IM} ^{0 °} from the second access 19b of the first mixing cell by its third input-output 25c and receives the signal S _FI ^{90 °} + S _{FI / IM-} ^{90 °} from the second port 22b of the fourth mixing cell by its second input-output 25b. Likewise, the signal S _FI ^{0 °} + S _{FI / IM} 0 ° issuing from the second port 20b of the second mixing cell 20 enters the seventh coupler 26 via its third input-output 26c and the signal S _FI ^{90 °} + S _{FI / IM} ^{-90 °} from the second port 21b of the third mixing cell enters its second input-output 26b. The signals entering through the third inputs-outputs 25c and 26c of the sixth and seventh couplers are phase shifted by 90 °. Thus, the following combinations are made:

• o for the sixth coupler 25, S _FI ^{0 ° + 90 °} + S _{FI / IM} ^{0 ° + 90 °} (third input / output 25c out of phase) with S _FI ^{90 °} + S _{FI / IM} ^{-90 °} (second input-output 25b not out of phase),
• o for the seventh coupler 26, S _FI ^{0 ° + 90 °} + S _{FI / IM} ^{0 ° + 90 °} (third input / output 26c phase shifted) with S _FI ^{90 °} + S _{FI / IM} ^{-90 °} (second input-output 26b not out of phase).

Since the powers between the inputs are substantially evenly distributed, it is therefore the signal S _FI ^{0 ° + 90 °} + S _{FI / IM} ^{0 ° + 90 °} + S _FI ^{90 °} + SFI / IM ^{-90 °} = S _FI ^{90 °} which leaves the first input-output 25a of the sixth coupler with a double output power than the signal S _FI ^{90 °} entered by the second input-output 25b of the sixth coupler, this thanks to the combination of the two signals inputted by the second and third input-outputs 25b and 25c. Since the seventh coupler 26 applies the same operation as the sixth coupler 25 on identical input signals, it is also a signal S _FI ^{90 °} which leaves the first input-output 26a of the sixth coupler. S _{FI / IM} signals were eliminated by the recombination of signals of substantially the same power S _{FI / IM} ^{90 °} and S _{FI / IM} ^{-90 °} in phase opposition. The mixer 9 thus operates a rejection of the image frequency during the reception phase.

Finally, the signals S _FI ^{90 °} from the first inputs-outputs 25a and 26a of the sixth and seventh couplers are recombined in the eighth coupler 27. These two signals are received by the first and second inputs-outputs 27a and 27b of the eighth coupler 27 and combine to exit on the output 9c of the mixer 9.

In summary, the signal S _RF + S _IM entering on the input-output 9a of the mixer 9 combined with the signal S _FOL entering on the first input 9b of the mixer 9 produces the signal S _FI ^{90 °} outgoing on the output 9c of the mixer 9. Frequency components Fol, RF and RF + Fol originating from the mixing cells 19, 21, 22 and then transmitted at the output 9c can then be easily filtered because of the large difference between these frequencies and Fl.

Phase shifts are applied using three groups of couplers. A first group consisting of the first and second couplers (14, 15) is a first means for phase shifting the signals from the local oscillator 12. A second group consisting of the third, fourth and fifth couplers (16, 17, 18) is a second means for phase shifting the RF frequency signals. A third group consisting of the sixth, seventh and eighth couplers (25, 26, 27) is a third means for phase shifting the IF frequency signals.

The figure 4 presents an exemplary embodiment of the invention with indications on the directions of signal propagation corresponding to the transmission phase.

• o sur le deuxième accès 19b de la première cellule de mélange 19, un signal S_FI ^-90° de fréquence FI déphasé de -90°,
• o sur le deuxième accès 22b de la quatrième cellule de mélange 22, un signal S_FI ^180° de fréquence FI déphasé de 180°,
• o sur le deuxième accès 21 b de la troisième cellule de mélange 21, un signal S_FI ^0° de fréquence FI non déphasé,
• o sur le deuxième accès 20b de la deuxième cellule de mélange 20, un signal S_FI ^90° de fréquence FI déphasé de 90°.

During this phase, an _IF signal S is sent to the mixer by its second input 9d. The eighth coupler 27 then distributes the signal S _FI on its first and second input-outputs 27a and 27b. The signal S _FI ^{180 °} from the first input-output 27a of the eighth coupler 27 is 180 ° out of phase with the input signal S _FI , while the signal S _FI ^{0 °} from the second input-output 27b of the eighth coupler 27 is not out of phase. The S _FI signal ^{180 °} then passes into the sixth coupler 25 via its first input-output 25a and the signal S _FI 0 ° enters the seventh coupler 26 by its first input-output 26a. At the end of the passage in these two couplers 25 and 26, the signals S _FI ^{180 °} and S _FI ^{0 °} are each divided again into two signals. The _SFI ^{180 °} and S _FI ^{0 °} signals from the second input-outputs 25b and 26b of the sixth and seventh couplers 25 and 26 are not out of phase while the signals S _FI ^{-90 °} and S _FI ^{90 °} respectively from the third Inputs-outputs 25c and 26c of the sixth and seventh coupler are phase shifted by 90 °. As previously described for the reception phase, the sixth and seventh couplers 25 and 26 are connected to the mixing cells 19, 20, 21, 22. The initial signal S _FI arriving at the second input 9d of the mixer 9 is thus distributed over the second access 19b, 22b, 21b, 20b of the mixing cells 19, 22, 21, 20 with a phase difference of 90 ° between each successive channel:

• o on the second port 19b of the first mixing cell 19, a signal S _FI ^{-90 °} of frequency IF shifted by -90 °,
• o on the second port 22b of the fourth mixing cell 22, a signal S _FI ^{180 °} of frequency IF shifted by 180 °,
• o on the second port 21 b of the third mixing cell 21, a signal S _FI ^{0 °} of frequency IF not out of phase,
• o on the second port 20b of the second mixing cell 20, a signal S _FI ^{90 °} IF frequency shifted by 90 °.

• o la première cellule 19 de mélange combine S_FI ^-90° sur le deuxième accès 19b avec S_FOL ^90° sur le premier accès 19a,
• o la deuxième cellule 20 de mélange combine S_FI ^90° sur le deuxième accès 20b avec S_FOL ^0° sur le premier accès 20a,
• o la troisième cellule 21 de mélange combine S_FI ^0° sur le deuxième accès 21 b avec S_FOL ^0° sur le premier accès 21 a,
• o la quatrième cellule 22 de mélange combine S_FI ^180° sur le deuxième accès 22b avec S_FOL ^90° sur le premier accès 22a.

Selon le fonctionnement d'une cellule de mélange décrit plus haut, les composantes fréquentielles en sortie des cellules de mélange sont FI, Fol, IM=Fol-FI, et RF=FI+Fol. Les composantes FI, Fol, et IM sont indésirables. La composante FI peut être filtrée aisément ultérieurement du fait de l'écart important entre FI et RF, elle sera donc ignorée dans la suite de la description. Par contre, les composantes Fol et IM sont potentiellement assez proches de RF pour notamment gêner un filtrage passe-bande autour de RF. Il faut donc les supprimer.
Ainsi, en sortie des cellules de mélange, on obtient :

• o sur le troisième accès 19c de la première cellule de mélange 19, S_FI+Fol ^-90°+90°+S_Fol-FI ^90°-(-90)°+S_Fol ^90° = S_RF ^0°+S_IM ^180°+S_Fol ^90°,
• o sur le troisième accès 20c de la deuxième cellule de mélange 20, S_FI+Fol ^90°+0°+S_Fol-FI ^0°-90°+S_Fol ^0° = S_RF ^90°+SM^-90°+S_Fol ^0°,
• o sur le troisième accès 21 c de la troisième cellule de mélange 21, S_FI+Fol ^0°+0°+S_Fol-FI ^0°-0°+S_Fol0°=S_RF ^0°+S_IM ^0°+S_Fol ^0°
• o sur le troisième accès 22c de la quatrième cellule de mélange 22, S_FI+Fol ^180°+90°+S_Fol-FI ^90°-180°+S_Fol ^90°=S_RF-^90°+S_IM ^-90°+S_Fol ^90°

In parallel, the local oscillator delivers, as for the reception phase, a signal S _FOL of frequency Fol which is transmitted and out of phase by the first and second couplers 14 and 15. Each mixing cell then receives two signals of frequencies FI and Crazy, but each with a different combination of phases. Indeed,

• the first mixing cell 19 combines S _FI ^{-90 °} on the second access 19b with S _FOL ^{90 °} on the first access 19a,
• the second mixing cell 20 combines S _FI ^{90 °} on the second access 20b with S _FOL ^{0 °} on the first access 20a,
• o the third mixing cell 21 combines S _FI ^{0 °} on the second access 21b with S _FOL ^{0 °} on the first access 21a,
• the fourth mixing cell 22 combines S _FI ^{180 °} on the second access 22b with S _FOL ^{90 °} on the first access 22a.

According to the operation of a mixing cell described above, the frequency components at the output of the mixing cells are F1, Fol, IM = Fol-IF, and RF = FI + Fol. FI, Fol, and IM components are undesirable. The component FI can be filtered easily later because of the large difference between FI and RF, it will be ignored in the following description. On the other hand, the components Fol and IM are potentially quite close to RF for interfering with a band-pass filtering around RF. So you have to delete them.
Thus, at the outlet of the mixing cells, we obtain:

• o on the third port 19c of the first mixing cell 19, S _{FI + Fol} ^{-90 ° + 90 °} + S _Fol-IF ^{90 ° - (- 90) °} + S _Fol ^{90 °} = S _RF ^{0 °} + S _IM ^{180 °} + S _Fol ^{90 °} ,
• o on the third port 20c of the second mixing cell 20, S _{FI + Fol} ^{90 ° + 0 °} + S _Fol-FI ^{0 ° -90 °} + S _Fol ^{0 °} = S _RF ^{90 °} + SM ^{-90 °} + S ^{0 °} _Fol ,
• o on the third port 21c of the third mixing cell 21, S _{FI + Fol} ^{0 ° + 0 °} + S _Fol-FI ^{0 ° -0 °} + S _Fol 0 ° = S _RF ^{0 °} + S _IM ^{0 °} + S _Fol ^{0 °}
• o on the third port 22c of the fourth mixing cell 22, S _{FI + Fol} ^{180 ° + 90 °} + S _Fol-FI ^{90 ° -180 °} + S _Fol ^{90 °} = S _RF - ^{90 °} + S _IM ^{-90 °} + S _Fol ^{90 °}

Following the same principle as in the reception phase, the signals are recombined in the third, fourth and fifth couplers 16, 17 and 18.
The signal S _RF ^{0 °} + S _IM ^{180 °} + S _Fol ^{90 °} leaving the third port 19c of the first mixing cell 19 is transmitted to the third coupler 16 via its third input-output 16c and is phase shifted by 90 °. The signal S _RF ^{90 °} + S _IM- ^{90 °} + S _Fol ^{0 °} leaving the third port 20c of the second mixing cell 20 is not out of phase. The third coupler 16 therefore operates the following combination:
(S _RF ^{0 ° + 90 °} + S _IM ^{180 ° + 90 °} + S _Fol ^{90 ° + 90 °} ) + (S _RF ^{90 °} + S _IM ^{-90 °} + S _Fol ^{0 °} ) and the signal from the first input-output 16a of the third coupler 16 is S _RF ^{90 °} + S _IM ^{-90 °} , with a power substantially equal to the sum of the input power. The Fol component was eliminated by the combination of phase opposition signals of approximately equal powers S _Fol ^{180 °} and S _Fol ^{0 °} . The same principle operates in the fourth coupler 17 with the following combination:
(S _RF + S _IM ^{0 ° 0 °} + S _Fol ^{0 °)} + (S _RF ^{-90 ° + 90} ° + S _IM ^{-90 ° + 90 °} + S _Fol ^{90 ° + 90 °).} The signal coming from the first input-output 17a of the third coupler 17 is therefore S _RF ^{0 °} + S _IM ^{0 °} , with a power substantially equal to the sum of the powers input. Here again, the combination of the input signals results in a rejection of the output frequency Fol.

The two signals coming from the first inputs-outputs 16a and 17a of the third and fourth couplers 16 and 17 are then recombined in the fifth coupler 18 passing respectively through the second and third input-outputs 18b and 18c. The following combination is then performed:
(S _RF ^{90 °} + S _λ ^{-90 °} ) + (S _RF ^{0 ° + 90 °} + _SMI ^{0 ° + 90 °} ). The powers on the second and third inputs-outputs 18b and 18c of the fifth coupler 18 being substantially equivalent, the fifth coupler 18 operates a rejection of the image frequency by combining the two components S _IM ^{-90 °} and S _Im ^{90 °} in opposition to phase. The signal from its first input-output 18a is S _RF ^{90 °} _.

In summary, the signal S _IF entering the second input 9d of the mixer 9 combined with the signal S _FOL entering the first input 9b of the mixer 9 produces the signal S _RF ^{90 °} outgoing on the input-output 9a of the mixer 9. The frequency components Fol and IM from the mixing cells are eliminated by judicious combinations of signals in phase opposition. The frequency F1 coming from the mixing cells and transmitted to the input-output 9a can then be easily filtered because of the large difference between RF and FI.

According to another embodiment, the local oscillator 12 can deliver a frequency Fol equal to RF + FI. In this case, the frequency transposition operated by the mixer again makes it possible to obtain an IF frequency signal at the output, but the image frequency to be eliminated is equal to Fol + FI and no longer to Fol-FI. The architecture of the mixer remains valid in this variant. Indeed, it is simply necessary to adapt the couplers to the frequency Fol and to interchange the connections to the first and fourth inputs-outputs 18d and 18a of the fifth coupler so as to pass the RF signal through the fourth input-output 18d. Preferably, a frequency Fol equal to RF-FI is chosen because it is generally easier to handle smaller frequencies.

An advantage of the invention is to directly operate the image rejection directly in the mixer. This avoids adding a filter, always penalizing in size on a circuit and sometimes even impossible to integrate on a MMIC.

Another advantage of the invention is to give the mixer a higher power linearity. Indeed, each mixing cell is subject to the saturation phenomenon of the output power when the input power becomes too large and then loses its linear characteristic. Each mixing cell is characterized in particular by its output power at the point of compression at 1 dB. As a reminder, the point of compression at 1 dB is, on a curve representing the power output as a function of the input power, the point at which the difference between the output power and its linear extrapolation is 1 dB. A mixer comprising four mixing cells 19, 20, 21 and 22 with the same 1 dB compression point in parallel, has a compression point 1 dB higher than that of each of the cells taken alone, thanks to the recombination of the powers in the output couplers 25, 26 and 27 in reception and in the couplers 16, 17 and 18 in transmission.

The figure 5 schematically an example of a circuit incorporating a single mixer for a communication application in millimeter range.

The circuit 50 comprises a bidirectional frequency mixer 9, a frequency multiplier 51, a low noise amplifier 52, a first voltage controlled amplifier 53, a coupling component 54, and a second voltage controlled amplifier 55.

The circuit 50 is composed of two main parts. The first part 50a includes the mixer 9, the low noise amplifier 52, the first amplifier 53 controlled by voltage, and the frequency multiplier 51. The second part 50b comprises the coupling component 54 and the second amplifier 55 controlled by voltage.

The first part 50a has elements that operate at frequencies in millimetric band, which allows to integrate this part of the circuit in a MMIC. The mixer 9 is connected to the frequency multiplier 51 receiving a signal produced by a local oscillator, connected to the low noise amplifier 52 receiving an antenna signal, connected to the first voltage controlled amplifier 53 for amplifying signals to be transmitted. , and connected to coupling component 54. In addition, the coupling component 54 receives signals at the IF intermediate frequency through the second voltage controlled amplifier 55, and also transmits signals at the IF frequency.

The coupling component 54 comprises the sixth, seventh, and eighth couplers 25, 26, 27 operating at the intermediate frequency FI. In the example described, the frequency FI is equal to 5 GHz. This frequency is too low to be able to place the second part 50b larger in integrated circuit, that is why the components of the second part 50b will for example be made from discrete components or lines distributed on printed circuit.

Claims (7)

Bidirectional signal mixer characterized in that it is adapted to operate in two modes: a reception mode, combining a radio signal S _{RF + IM} comprising a frequency component RF and an image frequency component IM with a signal S _FOL of frequency F _OL to produce an _IF signal of IF intermediate frequency, o a transmission mode, combining an intermediate frequency IF signal S _IF with a frequency signal S _FOL F _OL to produce a radioelectric signal S _RF, the mixer comprising at least: four mixing cells (19, 20, 21, 22) each adapted to combine two signals to produce an output signal transposed in frequencies with respect to the first of the two signals, a first phase shift means (14, 15) adapted to distribute the signal S _FOL on each mixing cell, a second phase shift means (16, 17, 18) adapted, in reception, to distribute the power of the signal S _{RF + IM} on each mixing cell, a third phase shift means (25, 26, 27) adapted, in reception, to combine the signals from said mixing cells to produce a signal S _FI free of the frequency component IM, the combined signals comprising IM image frequency components in phase opposition and IF frequency components in phase, the third phase-shifting means being also adapted, in transmission, to distribute the power of the signal S _FI on each mixing cell, and, the second phase-shifting means being also adapted, in transmission, to combine the signals coming from said mixing cells to producing a radio signal S _RF free of the frequency component F _OL , the combined signals comprising frequency components F _OL in opposite phase and RF frequency components in phase. Bidirectional signal mixer according to claim 1, characterized in that the first phase shift means comprises at least one coupler adapted to distribute the power of an input signal on two output signals, the first output signal SFOL ^{90 °} being out of phase with the second output signal S _FOL ^{0 °} . Bidirectional signal mixer according to one of the preceding claims, characterized in that the first phase shift means comprises a power divider (24) and two couplers (14, 15), said divider distributing the power of the signal S _FOL on an input each coupler, each coupler distributing the power of its incoming signal on two output signals, the first output signal S _FOL ^{90 °} being out of phase with the second signal S _FOL ^{0 °} output. Bidirectional signal mixer according to one of the preceding claims, characterized in that the second phase shift means comprises at least three couplers (16, 17, 18), a first input-output (18b) of the first coupler being connected to an input output (17a) of the second coupler, and a second input-output (18c) of the first coupler being connected to an input-output (17a) of the third coupler, the second and third couplers being connected to the mixing cells, in order to: o distributing, at the output of the second and third couplers, the power of the signal S _{RF + IM} received by an input-output (18a) of the first coupler, and / or combining the signals received by the second and third couplers to produce an S _RF signal on an input-output (18a) of the first coupler. Bidirectional signal mixer according to one of the preceding claims, characterized in that the third phase shift means comprises at least three couplers (25, 26, 27), a first input-output (27a) of the first coupler being connected to an input output (25a) of the second coupler, and a second input-output (27b) of the first coupler being connected to an input-output (26a) of the third coupler, the second and third couplers being connected to the mixing cells, in order to: o distributing, at the output of the second and third couplers, the power of the signal S _FI received by an input-output (9d) of the first coupler, and / or combining signals received by the second and third couplers to produce an _IF signal on an input-output (9c) of the first coupler. Method for mixing signals, characterized in that it uses a bidirectional mixer according to any one of the preceding claims to perform at least the following steps: over a duration Δt1, combining an RF frequency input signal with a frequency input signal Fol in order to output an IF frequency signal, over a time Δt2, shifted in time with respect to Δt1, combining an input signal of frequency F1 with a frequency input signal Fol in order to produce an output of an RF frequency signal. Radiofrequency transceiver system (50) comprising at least one bidirectional signal mixer according to one of Claims 1 to 5.

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